Method for manufacturing a semiconductor device

ABSTRACT

Provided are an etching method which uses an additive gas stably suppliable also in future, is reduced in the problem of particle contamination, is free from the problem of removability of side-wall protection film and has high shape controlling capacity, and a manufacturing method a highly-reliable semiconductor device by using this etching method. This etching method comprises depositing metal film including an aluminum over a semiconductor device and etching the metal film with a plasma of a mixture gas containing a Cl 2  gas, a BCl 3  gas and a CH 2 Cl 2  gas.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a manufacturing method of a semiconductor device, particularly to a manufacturing method of a semiconductor device, which comprises, during manufacture of the semiconductor device, plasma etching metal films including aluminum (Al).

[0002] In plasma etching of a metal material, it is the common practice to use a plasma of a mixture gas of Cl₂ and BCl₃ which are leading etching gases.

[0003] For microfabrication process, in addition to such gases, a CCl₄ gas, a CHCl₃ gas, an N₂ gas, a CHF gas or a gas obtained by diluting a flammable and explosive CH gas to not greater than an explosion limit is usually added as a shape controlling gas, in other words, as an under cut preventive gas. In Japanese Patent Application Laid-Open No. 251984/1997, proposed is a method of adding a CHBr gas as a shape controlling gas.

[0004] Among the shape controlling gases to be added upon plasma etching of a metal material, production of a CCl₄ gas is limited because it is an ozone depleting substance. Production of a CHCl₃ gas tends to be decreased owing to its carcinogenicity.

[0005] In a gas such as CHF gas containing an F element, AlF generated upon etching reaction forms particles having a large particle size. These particles cause a yield reduction so that this gas is not suited for mass production. Also in the case of an N₂ gas, AlN generated upon etching reaction forms particles so that it is not suited for mass production.

[0006] A Br-containing gas such as CHBr gas forms, on the side walls of a minute pattern during etching, a markedly strong side-wall protection film for shape control. This side-wall protection film cannot be removed by treatment with a chemical liquid. A diluted CH gas,on the other hand, contains only several percent of a C element having a shape controlling action so that it is accompanied with such a drawback as small shape controlling effects.

SUMMARY OF THE INVENTION

[0007] An object of the present invention is to provide an etching method which uses a gas suppliable stably also in future, is reduced in the problem of particle contamination, is free from the difficulty in removal of side-wall protection films, and has high shape controlling capacity, and a manufacturing method of a highly reliable semiconductor device by using this etching method.

[0008] In the present invention, a CH₂Cl₂ gas is used as an additive gas for shape control. Described specifically, a metal material is etched by a plasma of a mixture of a Cl₂ gas, a BCl₃ bas and a CH₂Cl₂ gas.

[0009] The specific and typical constitution of the present invention will next be described. In one aspect of the present invention, there is thus provided a manufacturing method of a semiconductor device which comprises depositing metal film including an aluminum over a semiconductor substrate and etching the metal film by using a plasma of a mixture of a Cl₂ gas, a BCl₃ gas and a CH₂Cl₂ gas.

[0010] In another aspect of the present invention, there is also provided a manufacturing method of a semiconductor device, which comprises, upon formation of multilayer interconnects of an aluminum-containing metal over a semiconductor substrate, etching of the metal interconnects by using a plasma of a mixture of a Cl₂ gas, a BCl₃ gas and a CH₂Cl₂ gas.

[0011] In a further aspect of the present invention, there is also provided a manufacturing method of a semiconductor device, which comprises forming metal films over a semiconductor substrate by stacking a TiN film, an Al film and a TiN film one after another; and etching the metal films by using a plasma of a mixture of a Cl₂ gas, a BCl₃ gas and a CH₂Cl₂ gas, wherein the amount of CH₂Cl₂ gas is adjusted to 0 to 4% upon etching of the TiN film, while it is adjusted to 5 to 30% during etching of the Al film.

[0012] In a still further aspect of the present invention, there is also provided a manufacturing method of a semiconductor device, which comprises depositing metal film including an aluminum over a semiconductor substrate, forming a resist mask over the metal film, etching the metal film by using a plasma of a mixture of a Cl₂ gas, a BCl₃ gas and a CH₂Cl₂ gas and removing a resist mask by using a plasma of a mixture containing an F element and an O element.

[0013] In a still further aspect of the present invention, there is also provided a manufacturing method of a semiconductor device, which comprises depositing metal film including an aluminum over a semiconductor substrate, forming patterns at a wiring pitch less than 500 nm over the metal film, and etching the metal film with a plasma of a mixture gas containing a Cl₂ gas, a BCl₃ gas and a CH₂Cl₂ gas.

[0014] In a still further aspect of the present invention, there is also provided a manufacturing method of a semiconductor device, which comprises depositing metal film including an aluminum over a semiconductor substrate, forming a first mask pattern group (or a first pattern group) at a first pitch and then, a second mask pattern group (or a second pattern group) at a second pitch over the metal film, and etching the metal film by using a plasma of a mixture of a Cl₂ gas, a BCl₃ gas and a CH₂Cl₂ gas.

[0015] In a still further aspect of the present invention, there is also provided a manufacturing method of a semiconductor device, which comprises forming metal films over a semiconductor substrate by stacking a TiN film, an Al film and a TiN film one after another, and etching the metal films by using a plasma of a mixture of a Cl₂ gas, a BCl₃ gas and, as an additive gas, a CH₂Cl₂ gas diluted with a diluting gas, wherein the mole concentration of the CH₂Cl₂ gas diluted with the diluting gas is 10% to 100%.

[0016] In a still further aspect of the present invention, there is also provided the above-described constitutions, wherein the pressure of the mixture gas is not greater than 1.5 Pa but 0.6 Pa or greater; the CH₂Cl₂ gas has a purity of at least 99.99%; and the plasma is generated using an electromagnetic wave having a frequency range of 300 MHz to 1 GHz (UHF range).

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 illustrates the characteristics of various additive gases;

[0018]FIG. 2 illustrates the relationship between a ratio of failure by particle contamination and the number of wafers treated;

[0019]FIG. 3 illustrates the relationship between the CD shift relative to a resist mask and the kind of additive gases;

[0020]FIG. 4 is a cross-sectional view, after washing treatment, of a sample etched with a CH₂Br₂-containing gas;

[0021]FIG. 5 is a cross-sectional view, after washing treatment, of a sample etched with the CH₂Cl₂-containing gas of the present invention;

[0022]FIG. 6 is a flow chart for explaining one example of a multilayer interconnection step of a semiconductor device to which the etching method of the present invention is applied;

[0023]FIG. 7A illustrates the cross-sectional structure of a sample used for metal etching, whereas FIG. 7B illustrates one example of the etching results of the sample (FIG. 7A);

[0024]FIG. 8 illustrates the relationship between a wiring pitch and undercut condition; and

[0025]FIG. 9 illustrates the relationship between the CD shift of patterns formed at a wiring pitch of 100 nm and a dilution ratio of CH₂Cl₂ when the sample of FIG. 7A is etched with a mixture gas containing a CH₂Cl₂ gas diluted with Ar.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1

[0026] Results of comparison between a CH₂Cl₂ gas and another gas in their characteristics such as ozone layer destructivity, carcinogenicity and inflammability are shown in FIG. 1.

[0027] A CH₂Cl₂ gas used in the present invention is, different from a CCl₄ gas or a CHF gas, free from the problem of ozone layer destruction and is, different from a CHCl₃ gas, has no carcinogenicity. There is accordingly a high possibility of it being supplied stably in future. Different from a CH gas or another CHCl gas, it is flame retardant so that it can be added without dilution. Different from a CHF gas or an N₂ gas, it does not contain elements such as N and F, which tends to make it free from the problem of particle contamination. Different from a CHBr gas, it does not contain Br so that it is presumed not to be troubled much with the problem in removability of a side-wall protection film.

[0028] Generation of particles was studied using a CH₄ gas diluted to 8% with Ar (which will hereinafter be described as “PR gas”), a CH₂Cl₂ gas, a CH₂Br₂ gas, a CHF₃ gas and an N₂ gas, respectively. In FIG. 2, shown is the relationship—when a wafer having a metal material thereon is etched with a plasma of each of various gases and a Cl₂-BCl₃ mixture gas—between a ratio of failure by particle contamination and the number of wafers treated. It is however to be noted that during etching, plasma cleaning in a chamber is conducted by using O₂ gas plasma discharge or Cl₂ gas plasma discharge.

[0029] When the number of the wafers etched with a plasma of a mixture gas containing an N₂ gas or a CHF₃ gas is 500, the failure ratio reaches 90% or greater. So this gas is not suited for mass production. When the number of the wafers treated with a plasma of a mixture gas containing a CH₂Cl₂ gas, a CH₂Br₂ gas or a PR gas is 5000, on the other hand, the failure ratio is suppressed to less than 10%, suggesting that this gas is suited for mass production.

[0030] In the next place, shape control was studied. A PR gas, a CH₂Cl₂gas, or a CH₂Br₂gas suited for mass production was selected as an additive gas, and a sample was etched using a plasma of a mixture gas containing the additive gas, a Cl₂ gas and a BCl₃ gas. The sample employed here was a wafer which had a diameter of 8 inches, had thereover TiN, Al and TiN films successively stacked one after another, and had a resist film formed over these stacked films. In FIG. 3, the relationship among a CD shift relative to the resist mask, an etching rate and kinds of gases added. In this diagram, an etching rate (nm/min) is indicated by a circle.

[0031] When the partial pressure of a Cl₂ gas is low, a decrease in an etching rate occurs. It is necessary to maintain the partial pressure of a Cl₂ gas at about 0.5 Pa or greater in order to maintain an etching rate at 600 nm/min or greater which is sufficient for practical use. Since high treating pressures cause an increase in the CD shift, it is necessary to suppress the treating pressure to 1.5 Pa or less in order to attain a practically usable CD shift of 100 nm or less. In addition, it is necessary to add a shape controlling gas in an amount of about 20% of the Cl₂ gas in order to suppress side etching.

[0032] In a PR gas, the shape controlling CH₄ gas has been diluted to 8%, so that the PR gas should be added in an amount of about 2.5 times as much as that of the Cl₂ gas in order to control the shape. This increases the treating pressure to about 3.5 times as much as the partial pressure of the Cl₂ gas, making it difficult to attain both a sufficient etching rate and a sufficient CD shift. Addition of a PR gas, which has been adjusted to maintain an etching rate at a practically usable level of 600 nm/min as shown in FIG. 3, increased a CD shift as large as several hundred nm or greater.

[0033] A CH₂Cl₂ gas or CH₂Br₂ gas is, on the other hand, usable without diluting a shape controlling gas. Even by the addition of a 20% shape controlling gas, the treating pressure can be suppressed to about 1.2 times as much as that of the Cl₂ partial pressure. This makes it possible to attain both a sufficient etching rate and sufficient CD shift within a wide range from 0.6 Pa to 1.5 Pa. As a result, a CH₂Cl₂ gas and a CH₂Br₂ gas can suppress the CD shift to about 10 nm while maintaining an etching rate at a practically usable level of 800 nm/min.

[0034] As described above, it has been found that a CH₂Cl₂ gas and a CH₂Br₂ gas are much superior in shape controllability to a PR gas.

[0035] After removal of the resist mask by a plasma of a CF₄ and O₂ mixture gas from the sample etched with each of a CH₂Cl₂ gas and CH₂Br₂ gas, the resulting wafer was washed with a mixed solution of acetic acid and aqueous ammonia. The cross-sectional views of the sample after washing are shown in FIGS. 4 and 5.

[0036] As is apparent from FIG. 4 wherein the shape after etching with a CH₂Br₂ gas is illustrated, a side-wall protection film 4 remains on the side walls of the barrier TiN layer 1, Al layer 2 and cap TiN layer 3 and over the cap TiN layer 3, suggesting that the side-wall protection film cannot be removed completely by the washing after etching. Indicated at numeral 5 in these diagrams is a semiconductor substrate.

[0037] As is apparent from FIG. 5 wherein the shape after etching with a CH₂Cl₂ gas is illustrated, the side-wall protection film is removed completely from the side walls of the barrier TiN layer 1, Al layer 2 and cap TiN layer 3 and from the upper surface of the cap TiN layer 3, suggesting that this gas is superior in removability of the side-wall protection film. For the removal of the resist mask, a plasma of a CF₄ and O₂ mixture gas was employed. Similar results are available insofar as the plasma is a mixture gas containing an F element and O element.

[0038] It has been understood from the above-described results that use of a CH₂Cl₂ gas as an additive gas for shape control is desired from four viewpoints, that is, stable gas supply, suitability for mass production, shape controllability and removability of side-wall protection films.

EXAMPLE 2

[0039] In etching of a stacked structure of a TiN film, an Al film and a TiN film formed over a semiconductor substrate, the amount of a CH₂Cl₂ gas is suppressed to 0 to 4% upon etching of the TiN film and it is increased to 5 to 30% only during etching of the Al film which needs shape control. This makes it possible to decrease the CD shift to half of that in the case of etching without changing the amount of the gas.

EXAMPLE 3

[0040]FIG. 6 illustrates an application example of the etching method of the present invention to a multilayer interconnection step of a semiconductor device. In this interconnection step, a via hole is made by successively carrying out (1) deposition of a silicon oxide film (TEOS) by chemical vapor deposition (CVD), (2) formation of a resist mask by photolithography and (3) etching of TEOS by using a plasma of a CF gas along the resist mask. In the resulting via hole, (4) TiN is embedded by sputtering, followed by (5) embedding of tungsten (W) by CVD.

[0041] Excessive W and TiN deposited over the TEOS surface by the above-described embedding step is (6) removed by chemical mechanical polishing (CMP) and then, (7) washed with a chemical solution. After successive deposition, over the TEOS surface after CMP, of (8) TiN by sputtering, (9) Al—Cu mixed crystals by sputtering, (10) TiN by sputtering, (11) TEOS by CVD, and (12) SiON by CVD, (13) the resist mask is patterned by lithography. Along this resist mask, TEOS is (14) etched by a CF gas to form a TEOS mask.

[0042] Along the TEOS mask thus formed, the TiN, Al—Cu and TiN films thus stacked are etched using a plasma of a mixture gas of Cl₂, BCl₃ and CH₂Cl₂ according to the present invention. After etching, the remaining resist mask is (16) removed by a plasma of a mixture gas of O₂ and CF₄, followed by (17) washing with a chemical solution.

[0043] After (18) deposition of an insulating material over the washed sample by CVD, the resulting sample is (19) planarized by CMP and then (20) washed with a chemical solution. The resulting sample is subjected to the above-described steps starting from (1) in repetition, whereby a multilayer interconnection is formed.

[0044] The yield of the semiconductor device produced in accordance with the method of the present invention which uses a CH₂Cl₂ gas for the etching step (15) was 90%. The yield of the semiconductor device produced using a PR gas in the step of (15) was, on the other hand, only 50% owing to disconnection failure or short-circuit failure. The yield lowered to 40% by the use of a CH₂Br₂ gas, because of high contact resistance. The yield drastically decreased to 10% by the use of a CHF₃ gas owing to particle contamination.

[0045] As described above, in the multi-layer interconnection step including an aluminum film, use of a plasma of a mixture gas of Cl₂, BCl₃ and CH₂Cl₂ for etching of a metal interconnection makes it possible to fabricate a semiconductor device having a high reliability.

EXAMPLE 4

[0046] As illustrated in FIG. 7A, a sample having various line and space patterns formed using a resist mask 6 over a stacked structure of a barrier TiN film 1, an Al film 2 and a cap TIN film 3 over a semiconductor substrate 5 was etched using a plasma of a mixture gas containing Cl₂, BCl₃ and an undercut preventive gas.

[0047] One example of the etched shape is shown in FIG. 7B.

[0048] Patterns of a wide pitch can be etched vertically, whereas those of a fine pitch have undercut appeared on the Al film 2.

[0049] In FIG. 8 illustrated are the results of the undercut conditions in the patterns formed at wiring pitches of 1000, 500, 300, 260 and 200 when a PR gas or CH₂Cl₂ gas was used as an additive gas. At wiring pitches of 500 nm or greater, no undercut was observed irrespective of the kind of the additive gas. At wiring pitches less than 500 nm, undercut appeared when a PR gas was added, while it was suppressed when a CH₂Cl₂ gas was added. This suggests that addition of a CH₂Cl₂ gas has marked effects on the patterns formed at a wiring pitch less than 500 nm.

EXAMPLE 5

[0050] A difference in the CD shift between the pattern formed at a wiring pitch of 1000 nm and that formed at a wiring pitch of 200 nm was measured using the sample obtained in Example 4. As a result, the difference in CD shift was as large as 200 nm in the case of PR gas addition, whereas it was as small as 20 nm in the case of CH₂Cl₂ gas addition. This suggests that addition of a CH₂Cl₂ gas is effective for etching of a sample on which patterns different in wiring pitch exist on the same wafer.

EXAMPLE 6

[0051] Upon preparation of the sample of Example 4, a CH₂Cl₂ gas having a purity of 99.9% was added, resulting in problems of foreign matters and metal contamination. It has been understood that such problems do not occur when a CH₂Cl₂ gas having a purity of 99.99% or greater is used.

EXAMPLE 7

[0052] The sample as illustrated in FIG. 7A was etched using a plasma of a mixture gas containing a Cl₂ gas, a BCl₃ gas and an undercut preventive gas. As this undercut preventive gas, a CH₂Cl₂ gas diluted with Ar was employed. In FIG. 9, the relationship between the CD shift of the patterns formed at a wiring pitch of 1000 nm and a dilution ratio of CH₂Cl₂ is illustrated.

[0053] The CD shift increases with a dilution ratio. At a mole concentration of CH₂Cl₂ not less than 10%, however, CD shift is smaller compared with the case where a PR gas is added. It has been found that when a CH₂Cl₂ is diluted with Ar to give a mole concentration of 10% to 100%, the shape controllability is higher, compared with the use of a conventional gas. For dilution, Ar was employed here, but there is no limitation imposed on the dilution gas insofar as it is inert.

EXAMPLE 8

[0054] The sample obtained in FIG. 7A was etched with a mixture gas of Cl₂, BCl₃ and CH₂Cl₂ by using each of an etching system which generates a plasma by using an UHF-range electromagnetic wave (300 MHz to 1 GHz) (which system will hereinafter be called “UHF plasma etching system), an etching system which generates a plasma by using an electromagnetic microwave (2.45 GHz) (which system will hereinafter be called “microwave etching system”, and an etching system which generates a plasma by using an RF-range electromagnetic wave (13.56 MHz or less) (which system will hereinafter be called “ICP plasma etching system).

[0055] As a result, the UHF plasma etching system did not cause undercut easily compared with the microwave plasma etching system or ICP etching system. In the microwave plasma etching system or ICP etching system, a plasma density is high and this facilitates dissociation of CH₂Cl₂ into the corresponding atoms so that effects of gas addition are reduced by half. It is presumed that in the UHF plasma etching system, on the other hand, a plasma density is low and this disturbs dissociation of a CH₂Cl₂gas, effects of the additive gas tend to appear readily.

EXAMPLE 9

[0056] In Example 3, the resist was removed in the step 16 after etching of the stacked films of TiN, Al—Cu and TiN in the step 15. In this Example, after etching of SION and TEOS in the step 14, the resist removal of the step 16 is conducted, followed by etching of the stacked films of TiN, Al—Cu, and TiN of the step 15. Even after such a permutation, similar results are available.

[0057] In Example 3, TEOS was deposited over TiN in the step 11. Similar results are available even if deposition of SiON over TiN in the step 12 is conducted without the step 11.

[0058] As described above, a highly reliable semiconductor device can be manufactured by using the manufacturing method of the present invention adopting an etching method which uses a gas suppliable stably also in future, is reduced in the problem of particle contamination, is free from the problem in the removal of a side-wall protection film and exhibits high shape controlling capacity. 

What is claimed is:
 1. A manufacturing method of a semiconductor device, which comprises depositing metal film including an aluminum over a semiconductor substrate, and etching the metal film with a plasma of a mixture gas containing a Cl₂ gas, a BCl₃ gas and a CH₂Cl₂ gas.
 2. A method of claim 1, wherein the pressure of the mixture gas is not greater than 1.5 Pa but 0.6 Pa or greater.
 3. A method of claim 1, wherein the CH₂Cl₂ gas has a purity of 99.99% or greater.
 4. A method of claim 1, wherein the plasma is generated using an electromagnetic wave within a frequency range of 300 MHz to 1 GHz.
 5. A manufacturing method of a semiconductor device, which comprises forming a multilayer interconnection of metals including aluminum over a semiconductor substrate, wherein upon etching of the metal multilayer interconnection, a plasma of a mixture gas containing a Cl₂ gas, a BCl₃ gas and a CH₂Cl₂ gas is used.
 6. A method of claim 5, wherein the pressure of the mixture gas is not greater than 1.5 Pa but 0.6 Pa or greater.
 7. A method of claim 5, wherein the CH₂Cl₂ gas has a purity of 99.99% or greater.
 8. A method of claim 5, wherein the plasma is generated using an electromagnetic wave within a frequency range of 300 MHz to 1 GHz.
 9. A manufacturing method of a semiconductor device, which comprises forming metal films by stacking a TiN film, an Al film and a TiN film successively over a semiconductor substrate, and etching the metal films with a plasma of a mixture gas of a Cl₂ gas, a BCl₃ gas and a CH₂Cl₂ additive gas, wherein the CH₂Cl₂ gas is added in an amount of 0 to 4% upon etching of the TiN film, whereas the amount of the CH₂Cl₂ gas is increased to 5 to 30% during etching of the Al film.
 10. A manufacturing method of a semiconductor device, which comprises depositing metal film including an aluminum over a semiconductor substrate, forming a resist mask over the metal film, etching the metal film with a plasma of a mixture gas of a Cl₂ gas, a BCl₃ gas and a CH₂Cl₂ gas, and removing the resist mask with a plasma of a mixture gas containing an F element and an O element.
 11. A manufacturing method of a semiconductor device, which comprises depositing metal film including an aluminum over a semiconductor substrate, forming patterns at a wiring pitch less than 500 nm over the metal film, and etching the metal film with a plasma of a mixture gas containing a Cl₂ gas, a BCl₃ gas and a CH₂Cl₂ gas.
 12. A manufacturing method of a semiconductor device, which comprises depositing metal film including an aluminum over a semiconductor substrate, forming, over the metal film, first mask patterns at a first wiring pitch and second mask patterns at a second wiring pitch wider than the first wiring pitch, and etching the metal films with a plasma of a mixture gas containing a Cl₂ gas, a BCl₃ gas and a CH₂Cl₂ gas.
 13. A manufacturing method of a semiconductor device, which comprises depositing metal film including an aluminum over a semiconductor substrate, forming, over the metal film, first patterns at a first wiring pitch and second patterns at a second wiring pitch wider than the first wiring pitch, and etching the metal film with a plasma of a mixture gas containing a Cl₂ gas, a BCl₃ gas and a CH₂Cl₂ gas.
 14. A manufacturing method of a semiconductor device, which comprises forming metal films over a semiconductor substrate by stacking a TiN film, an Al film and a TiN film one after another, and etching the metal films with a plasma of a mixture gas containing a Cl₂ gas, a BCl₃ gas and an additive gas obtained by diluting a CH₂Cl₂ gas with a dilution gas, wherein the mole concentration of the CH₂Cl₂ gas after dilution with the dilution gas is 10% to 100%.
 15. A manufacturing method of a semiconductor device, which comprises depositing metal film including an aluminum over a semiconductor substrate, and etching the metal film with a plasma formed, in a plasma etching system for generating a plasma by using an UHF-range electromagnetic wave, from a mixture gas containing a Cl₂ gas, a BCl₃ gas and a CH₂Cl₂ gas. 